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Old 18th April 2006, 09:01 AM   #1
Antonix is offline Antonix  Italy
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Default old bjt amplifier kit

I have 4 bjt amplifier kit and i want to make some little optimization to improve sound quality and performance with 4ohm load.

Any suggestion on it ?
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Old 18th April 2006, 09:02 AM   #2
Antonix is offline Antonix  Italy
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The power supply are 50 0 - 50V and the power rated is 100Wrms 8ohm.
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Old 18th April 2006, 04:06 PM   #3
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If you want to drive 4 Ohm speakers it would be a very good idea to add at least one extra set of output transistors
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Old 19th April 2006, 08:02 AM   #4
Antonix is offline Antonix  Italy
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Quote:
Originally posted by ACD
If you want to drive 4 Ohm speakers it would be a very good idea to add at least one extra set of output transistors
Yes but I can't mount others output transistors.

I want to make make a little optimization to make a little more stable the output and drivers stage.

What do you think about a 100nF capacitor on E - C of Q1
and a 39pF capacatitors on B - C of Q2 and Q3 ?
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Old 19th April 2006, 12:54 PM   #5
djk is offline djk
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"What do you think about a 100nF capacitor on E - C of Q1 "

I would do 1µF across R7, R8 instead.

I would also use a better opamp, not too fast. A NE5534 with the correct cap would sound much better.

Bypass C4, 5, 7 with 100nF.

I would rather see R10, 11 fed from the stabilized opamp supplies. The values would need to be lowered to keep the current up.

I did a commercial design of a CFP output stage with gain, driven from an opamp, about 10 years ago. It sounded quite good.
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Old 19th April 2006, 01:20 PM   #6
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Why don't you check out Jan's amp? The same idea but a little bit developed.
http://www.delta-audio.com/PA-34A.htm
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Old 19th April 2006, 01:38 PM   #7
djk is offline djk
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Not very similar, but I like the Baker clamp with the LEDs.
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Old 20th April 2006, 04:38 AM   #8
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Default very interested !!!

Hi, Antonix do you have sample PCB ?
I have some idea for improve this similar circuit with error phase correction topology.

Regard
analog guy
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Old 21st April 2006, 11:32 AM   #9
edl is offline edl  Hungary
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Here is my amp design with OPA frontend. Cheap, simple, but powerful and sounds nice.

schema: http://edl.uw.hu/sch.jpg
parts list: http://edl.uw.hu/parts.jpg
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